The aging kidney: insights from experimental studies.

The rat provides a useful experimental model to study of the mechanisms of kidney aging. As in man, a wide diversity in the renal response to aging occurs in the rat, and because of this variability it is important to always specify experimental conditions, i.e., strain, gender, diet, and environment. Most aging rats display chronic progressive nephrosis, although the rate at which injury develops is highly variable. There are a number of known risk factors that potentiate injury, including male gender, genetic background, obesity, high protein/high calorie diet, and environmental exposure to pathogens. The causes of age-dependent glomerulopathy are multifactorial and include an imbalance between synthesis and degradation of extracellular matrix products, as well as hemodynamic alterations. Of importance, this damage is not inevitable and can be dissociated from normal kidney aging when optimal conditions for successful aging are provided. There is complex and sometimes contradictory information on vasoactive factors. It is, likely, however, that the activity of intrarenal AngII is somehow upregulated in the aging kidney of some, but not all, strains, and alpha 1-dependent renal nerve activity may also be enhanced. The endothelial vasodialtory prostaglandins and NO exert an increasingly important role in the maintenance of renal perfusion with advancing age, although their production may be diminished. In the future, we anticipate that comparison of rats with different genetic backgrounds will help to dissociate true aging from disease.